Polymerization of lactides and lactones, 12. Synthesis of poly[(glycolic acid)‐alt‐(L‐glutamic acid)] and poly{(lactic acid)‐co‐[(glycolic acid)‐alt‐(L‐glutamic acid)]}

Glutamic acid/glycolic acid‐based biodegradable polymers have been prepared by ring‐opening polymerization of (3S)‐3‐[(benzylcarbonyl)ethylene] morpholine‐2,5‐dione, and the copolymerization of the morpholine‐2,5‐dione derivative and lactide. The homopolymerization and copolymerization were carried out in bulk at 140°C with SnOct₂ as a catalyst to give the corresponding protected poly(Glc‐alt‐Glu) and protected poly[LA‐co‐(Glc‐alt‐Glu)], respectively. After removal of the protective group by catalytic hydrogenation with Pd/C (5%) as a catalyst, poly(Glc‐alt‐Glu) and poly[LA‐co‐(Glc‐alt‐Glu)] showed excellent hydrophilicity.     

Synthesis and characterization of new ABA triblock copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] and poly(ethylene oxide) blocks

ABA type block copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] (PIBMD, A) and poly(ethylene oxide) (M_n = 6 000, PEO, B) blocks, PIBMD-b-PEO-b-PIBMD, were synthesized via ring-opening polymerization of 3(S)-isobutylmorpholine-2,5-dione in the presence of hydroxytelechelic poly-(ethylene oxide) with stannous octoate as a catalyst. M_n of the resulting copolymers increases with increasing 3(S)-isobutylmorpholine-2,5-dione content in the feed at constant mole ratio of monomer (M) to catalyst (C) (M/C = 125). No racemization of the leucine residue takes place during both homopolymerization of IBMD and polymerization of IBMD in the presence of PEO and Sn(Oct)₂. The melting temperature of the PIBMD segments in the block copolymers depends on the length of the PIBMD blocks. The melting temperature of the PEO blocks is lower than that of the homopolymer, and the crystallinity of the PEO block decreases with increasing length of the PIBMD blocks. The PIBMD block crystallizes first upon cooling from the melt. This leads to only imperfect crystallization or no crystallization of the PEO blocks.     

Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers

We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr₂(PPh₃)₂, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.

SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.     

The Aggregation Behavior of Poly(ethylene oxide)‐Poly(methyl methacrylate) Diblock Copolymers in Organic Solvents

Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(deuteromethyl methacrylate) block copolymers have been prepared by group transfer polymerization of methyl methacrylate (MMA) and deuteromethyl methacrylate (MMA‐d₈), respectively, using macroinitiators containing poly(ethylene oxide) (PEO). Static and dynamic light scattering and surface tension measurements were used to study the aggregation behavior of PEO‐PMMA diblock copolymers in the solvents tetrahydrofuran (THF), acetone, chloroform, N,N‐dimethylformamide (DMF), 1,4‐dioxane and 2,2,2‐trifluoroethanol. The polymer chains are monomolecularly dissolved in 1,4‐dioxane, but in the other solvents, they form large aggregates. Solutions of partially deuterated and undeuterated PEO‐PMMA block copolymers in THF have been studied by small‐angle neutron scattering (SANS). Generally, large structures were found, which cannot be considered as micelles, but rather fluctuating structures. However, ¹H NMR measurements have shown that the block copolymers form polymolecular micelles in THF solution, but only when large amounts of water are present. The micelles consist of a PMMA core and a PEO shell.     

Allyl End‐Functionalized Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) Block Copolymers: Synthesis,Characterization, and Chemical Modification

Summary: Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) block copolymer (PEO‐b‐PMM 2.1.2) bearing an allyl moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2). This allyl functional group was subsequently modified by reaction with thiol‐bearing functional groups to generate carboxyl and amino functionalized biodegradable block copolymers. These end‐group reactions, performed in good yields both in organic media and in aqueous micellar solutions, lead to functionalized PEO‐b‐PMM 2.1.2 copolymers which are of interest for cell targeting purposes.

Synthetic route to α‐allyl functionalized PEO‐b‐PMM 2.1.2 copolymers.     

SET‐LRP Synthesis of Well‐Defined Light‐Responsible Block Copolymer Micelles

Herein, the synthesis of well‐defined light‐sensitive amphiphilic diblock copolymers consisting of UV‐responsive poly(2‐nitrobenzyl acrylate) (PNBA) and hydrophilic poly(ethylene oxide) (PEO) blocks is reported. This is achieved by a single electron transfer living radical polymerization (SET‐LRP) of 2‐nitrobenzyl acrylate monomer initiated by PEO‐containing macroinitiator. Despite several reports on PEO‐b‐PNBA copolymers, this is the first time the PNBA block is synthesized by a controlled radical polymerization leading to the copolymers with low dispersity (Ð = 1.10). In water, the copolymers self‐assemble into well‐defined micelles with a hydrodynamic diameter of 25 nm. Upon irradiation with UV‐light, the PNBA units degrade to hydrophilic poly(acrylate) resulting in disassembly of the micelles. Considering the robustness of the reported synthetic protocol, the prepared polymers represent an interesting platform for the construction of new stimuli‐responsive drug delivery systems.     

β‐Cyclodextrin‐Based Star Amphiphilic Copolymers: Synthesis,Characterization, and Evaluation as Artificial Channels

14‐arm amphiphilic star copolymers are synthesized according to different strategies. First, the anionic ring polymerization of 1,2‐butylene oxide (BO) initiated by per(2‐O‐methyl‐3,6‐di‐O‐(3‐hydroxypropyl))‐β‐CD (β‐CD’OH₁₄) and catalyzed by t‐BuP₄ in DMF is investigated. Analyses by NMR and SEC show the well‐defined structure of the star β‐CD’‐PBO₁₄. To obtain a 14‐arm poly(butylene oxide‐b‐ethylene oxide) star, a Huisgen cycloaddition between an α‐methoxy‐ω‐azidopoly(ethylene oxide) and the β‐CD’‐PBO₁₄,whose end‐chains are beforehand alkyne‐functionalized, is performed. In parallel, 14‐arm star copolymers composed of butylene oxide‐b‐glycidol arms are successfully synthesized by the anionic polymerization of ethoxyethylglycidyl ether (EEGE) initiated by β‐CD’‐PBO₁₄ with t‐BuP₄. The deprotection of EEGE units is then performed to provide the polyglycidol blocks. These amphiphilic star polymers are evaluated as artificial channels in lipid bilayers. The effect of changing a PEO block by a polyglycidol block on the insertion properties of these artificial channels is discussed.     

Syndiospecific Living Block Copolymerization of Styrenic Monomers Containing Functional Groups,and Preparation of Syndiotactic Poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]}

At –25°C, the sequential block copolymerizations of 4‐(tert‐butyldimethylsilyloxy)styrene (TBDMSS) and 4‐methylstyrene (4MS) were investigated by using a syndiospecific living polymerization catalyst system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃) and tris(pentafluorophenyl)borane (B(C₆F₅)₃). The number‐average molecular weight (M̄_n) of the poly(TBDMSS)s increased linearly with increasing the polymer yield up to almost 100 wt.‐% consumption of TBDMSS used as 1^st monomer. The M̄_n value of the polymer after the second monomer (4MS) addition continued to increase proportionally to the polymer yield. The molecular weight distributions (MWDs) of the polymers remained constant at around 1.05–1.18 over the entire course of block copolymerization. It was concluded that the block copolymerizations of TBDMSS and 4MS with the Cp*TiMe₃ /B(C₆F₅)₃ /AlOct₃ catalytic system proceeded with a high block efficiency. The ¹³C NMR analysis clarified that the block copolymers obtained in this work had highly syndiotactic structure. By the deprotection reaction of silyl group with conc. hydrochloric acid (HCl), syndiotactic poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]} (poly[HOST‐b‐(4MS‐co‐HOST)]) was successfully prepared.     

Poly(hydroxyl propyl methacrylate)‐b‐Poly(oligo ethylene glycol methacrylate) Thermoresponsive Block Copolymers by RAFT Polymerization

Thermoresponsive amphiphilic poly(hydroxyl propyl methacrylate)‐b‐poly(oligo ethylene glycol methacrylate) block copolymers (PHPMA‐b‐POEGMA) are synthesized by RAFT polymerization, with different compositions and molecular weights. The copolymers are molecularly characterized by size‐exclusion chromophotography, and ¹H NMR spectroscopy. Dynamic light scattering (DLS) and static light scattering (SLS) experiments in aqueous solutions show that the copolymers respond to temperature variations via formation of self‐organized nanoscale aggregates. Aggregate structural characteristics depend on copolymer composition, molecular weight, and ionic strength of the solution. Fluorescence spectroscopy experiments confirm the presence of less hydrophilic domains within the aggregates at higher temperatures. The thermoresponsive behavior of the PHPMA‐b‐POEGMA block copolymers is attributed to the particular solubility characteristics of the hydrophilic, water insoluble PHPMA block that are modulated by the presence of the water soluble POEGMA block.     

Association Behavior between End‐Functionalized Block Copolymers PEO‐PPO‐PEO and Poly(acrylic acid)

Summary: The end groups of ABA‐triblock copolymers HO–PEO–PPO–PEO–OH, (PEO – poly(ethylene oxide), PPO – poly(propylene oxide)), have been modified with ammonia, ethylene diamine and linear polyethylenimine (LPEI) by substitution of the α,ω‐ditosyl ester of the triblock copolymer (TsO–PEO–PPO–PEO–OTs) with amines, or by the hydrolysis of the corresponding poly(2‐methyl‐2‐oxazoline) (PMeOx) containing ABCBA block copolymers. The latter block copolymer structures have been obtained by the polymerization of MeOx using TsO–PEO–PPO–PEO–OTs as a macro‐initiator. Adding poly(acrylic acid) (PAA) to these (poly)amine terminated block copolymers leads to the formation of networks through a combination of PAA–PEO hydrogen bonding and PAA–(poly)amine acid‐base reaction. Depending on the number of amino groups at both chain ends of the block copolymer, the corresponding complexes behave as liquids, gels or precipitates. Introduction of as little as 1–5 wt.‐% block copolymers H₂N–PEO–PPO–PEO–NH₂ or H₂NCH₂CH₂NH–PEO–PPO–PEO–NHCH₂CH₂NH₂ to the system of HO–PEO–PPO–PEO–OH/PAA leads to viscous liquids with strong shear‐thickening behavior.

Reversible gel formation via the ternary PAA/HO–PEO–PPO–PEO–OH/H₂N–PEO–PPO–PEO–NH₂ system under shear conditions.     

Molecular Mass Characteristics of (2‐Benzothiazolon‐3‐yl)acetic Acid–Telechelic Poly(ethylene oxide)s Determined by MALDI‐TOF Mass Spectrometry and SEC

(2‐benzothiazolon‐3‐yl)acetic acid–telechelic poly(ethylene oxide)s (1 100–4 440 Da) with narrow molecular mass distributions (MMD) were analysed by matrix‐assisted laser desorption‐ionisation time‐of‐flight mass spectrometry (MALDI‐TOF MS) and size exclusion chromatography (SEC). The average molecular masses (M̄_n and M̄_w) determined by both methods were compared and a good agreement established. The cutting of the low molecular part of the initial poly(ethylene glycol) MMD during purification and isolation of the produced telechelic poly(ethylene oxide)s was proved. For this reason, the degree of esterification (x) of poly(ethylene glycol) (PEG) with (2‐benzothiazolon‐3‐yl)acetic acid was calculated by MALDI‐TOF MS and SEC, using additional UV data. The two series of x values derived from the M̄_n‐values, determined by the two methods, are very close. All of them are less than unity and the differences between the two types of x values decrease with the PEG molecular mass growth.     

Synthesis of 6‐Armed Amphiphilic Block Copolymers with Styrene and 2,3‐Dihydroxypropyl Acrylate by Atom Transfer Radical Polymerization

The controlled free radical polymerization of (2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methyl acrylate (DMDMA) was achieved by atom transfer radical polymerization (ATRP) in tetrahydrofuran (THF, 50%, v/v) solution at 90°C with the discotic six‐functional initiator, 2,3,6,7,10,11‐hexakis(2‐bromobutyryloxy) triphenylene (HBTP). The 6‐armed polyDMDMA with low polydispersity index (M̄_w/M̄_n = 1.52–1.32) was obtained. The copolymerization of DMDMA with styrene (St) using 6‐armed polySt‐Br as macroinitiator was carried out, and the GPC traces of the copolymers obtained were unimodal and symmetrical, indicating complete conversion of the macroinitiator into block copolymer. The star‐shaped block copolymers with different segment compositions and narrower polydispersity (1.21–1.24) were synthesized, and subsequent hydrolysis of the acetal‐protecting group in 1 N HCl THF solution produced poly[St‐b‐(2,3‐dihydroxypropyl)acrylate] [poly(St‐b‐DHPA)], which was verified by IR and NMR spectroscopy.     

Crystallization in ABC Triblock Copolymers with Two Different Crystalline End Blocks: Influence of Confinement on Self‐Nucleation Behavior

The influence of different confinements active during crystallization within polybutadiene‐block‐polyisoprene‐block‐poly(ethylene oxide) (PB‐b‐PI‐b‐PEO) and the corresponding hydrogenated polyethylene‐block‐poly(ethylene‐alt‐propylene)‐block‐poly(ethylene oxide) (PE‐b‐PEP‐b‐PEO) triblock copolymers on the self‐nucleation behavior of the crystallizable PEO and PE blocks is investigated by means of differential scanning calorimetry (DSC). In triblock copolymers with PEO contents ≤ 20 wt.‐% crystallization of PEO is confined within small isolated microdomains (spheres or cylinders), and PEO crystallization takes place exclusively at high supercoolings. Self‐nucleation experiments reveal an anomalous behavior in comparison to the classical self‐nucleation behavior found in semicrystalline homopolymers. In these systems, domain II (exclusive self‐nucleation domain) vanishes, and self‐nucleation can only take place at lower temperatures in domain III_SA, when annealing is already active. The self‐nucleation behavior of the PE blocks is significantly different compared with that of the PEO blocks. Regardless of the low PE content (10–25 wt.‐%) in the investigated PE‐b‐PEP‐b‐PEO triblock copolymers a classical self‐nucleation behavior is observed, i.e., all three self‐nucleation domains, usually present in crystallizable homopolymers, can be located. This is a direct result of the small segmental interaction parameter of the PEP and PE segments in the melt. As a consequence, crystallization of PE occurs without confinement from a homogeneous mixture of PE and PEP segments.

Self‐nucleation regimes of a block copolymer showing confined crystallization by means of DSC.     

Poly(ε‐caprolactone) Single Crystals with Different Aspect Ratios Mediated by Counterion Exchange on the Basis of Hofmeister Series

Although polymeric single crystals fabricated from self‐assembly of block copolymers are reported, preparation of single crystals with different aspect ratios still remains a major challenge. In this work, a facile way is demonstrated to prepare poly(ε‐caprolactone) based single crystals with tunable aspect ratios through simple counterion exchange on the basis of the Hofmeister series. Briefly, after ion exchange from Brˉ (an ion‐containing triblock copolymer, poly(ethylene oxide)‐b‐poly(ε‐caprolactone)‐b‐poly(quaternized 2‐(dimethylamino)ethyl methacrylate)/ethyl bromide (PEO‐b‐PCL‐b‐qPDM‐Br)) to more hydrophobic anions, Iˉ, SCNˉ, PF₆ˉ and OTfˉ, respectively, morphological transitions from spheres to wormlike micelles and sphere to 2D platelet structure with an increasing aspect ratio are observed. The morphological transition depends on the essential hydrophilicity of the qPDM‐X segment and increasing crystallinity of the PCL core caused by ion exchange. These findings provide a facile approach to the preparation of polymeric single crystals with tunable aspect ratios.     

Tunable Morphologies From Bulk Self‐Assemblies of Poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) Triblock Copolymers

Reactive poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) (PAPTES‐b‐PS‐b‐PAPTES) triblock copolymers are prepared through nitroxide‐mediated polymerization (NMP). The bulk morphologies formed by this class of copolymers cast into films are examined by small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The films morphology can be tuned from spherical structures to lamellar structures by increasing the volume fraction of PS in the copolymer. Thermal annealing at temperatures above 100 °C provides sufficient PS mobility to improve ordering.     

Spherical Compound Micelles with Lamellar Stripes Self‐Assembled from Star Liquid Crystalline Diblock Copolymers in Solution

Detailed investigations on the self‐assembly of amphiphilic star block copolymers composed of three‐arm poly(ethylene oxide) (PEO) and poly(methacrylate) (PMAAz) with an azobenzene side chain (denoted as 3PEO‐b‐PMAAz) into stable spherical aggregates with clear lamellar stripes in solution are demonstrated. Four block copolymers, 3PEO₁₂‐b‐PMA(Az)₃₃, 3PEO₂₂‐b‐PMA(Az)₃₁, 3PEO₂₂‐b‐PMA(Az)₆₂, and linear PEO₆₈‐b‐PMA(Az)₃₁, are synthesized. The liquid crystalline properties of the block copolymers are studied by differential scanning calorimetry, polarized optical microscopy techniques, and wide‐angle X‐ray diffraction. The morphologies of the compound micelles self‐assembled in tetrahydrofuran (THF)/water mixtures are observed by means of transmission electron microscopy and scanning electron microscopy. The size of the spherical micelles is influenced by the self‐assembly conditions and the lengths of two blocks. The well‐defined three‐arm architecture of the hydrophilic blocks is a key structural element to the formation of stable spherical compound micelles. The micelle surface integrity is affected by the lengths of PEO blocks. The lamellar stripes are clearly observed on these micelles. This work provides a promising strategy to prepare functional stable spherical compound micelles self‐assembled by amphiphilic block copolymers in solution.     

Synthesis and Self‐Assembly Behavior of Organic–Inorganic Poly(ethylene oxide)‐block‐Poly(MA POSS)‐block‐Poly(N‐isopropylacrylamide) Triblock Copolymers

In this work, the synthesis of 3‐methacryloxypropylheptaphenyl POSS, a new POSS macromer (denoted MA‐POSS) is reported. The POSS macromer is used to synthesize PEO‐b‐P(MA‐POSS)‐b‐PNIPAAm triblock copolymers via sequential atom transfer radical polymerization (ATRP). The organic‐inorganic, amphiphilic and thermoresponsive ABC triblock copolymers are characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) show that the hybrid ABC triblock copolymers are microphase‐separated in bulk. Cloud point measurements show that the effect of the hydrophiphilic block (i.e. PEO) on the LCSTs is more pronounced than the hydrophobic block (i.e. P(MA‐POSS)). Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) show that all the triblock copolymers can be self‐organized into micellar aggregates in aqueous solutions. The sizes of the micellar aggregates can be modulated by changing the temperature. The temperature‐tunable self‐assembly behavior is interpreted using a combination of the highly hydrophobicity of P(MA‐POSS), the water‐solubility of PEO and the thermoresponsive property of PNIPAAm in the triblock copolymers.     

Graft Copolymers with Complex Polyether Structures: Poly(ethylene oxide)‐graft‐Poly(isobutyl vinyl ether) by Combination of Living Anionic and Photoinduced Cationic Graft Polymerization

A novel polymerization mechanism transformation strategy, involving anionic ring‐opening polymerization and photoinduced cationic polymerization, is successfully applied for the synthesis of poly(ethylene oxide)‐graft‐poly(isobutyl vinyl ether) (PEO‐g‐PIBVE). First, poly(ethylene oxide‐co‐ethoxyl vinyl glycidyl ether) [P(EO‐co‐EVGE)] is synthesized by living anionic polymerization. The vinyl moieties of the functional PEO‐based polymer are converted to the hydrogen iodide adduct by photolysis of diphenyliodonium iodide, monitored using NMR spectroscopy. A modified mode of Lewis acid‐catalyzed living cationic polymerization is performed as a “grafting from” method to generate PIBVE segments grafted onto the PEO main chain. Both the intermediates and the final graft copolymers are characterized by gel‐permeation chromato­graphy (GPC) and ¹H NMR analysis.

     

Miscibility of C60‐end‐capped poly(ethylene oxide) with poly(p‐vinylphenol)

A fullerene (C₆₀)‐end‐capped poly(ethylene oxide) (FPEO) has been prepared by the cycloaddition reaction of monoazido‐terminated poly(ethylene oxide) with C₆₀. The majority of the FPEO sample is the monoadduct as shown by thermogravimetry and X‐ray photoelectron spectroscopy. Most electronic characteristics of C₆₀ are retained in the polymer as shown by its UV‐visible absorption spectrum. The incorporation of C₆₀ reduces the extent of crystallinity of PEO by 17%. The miscibility behavior of FPEO with poly(p‐vinylphenol) (PVPh) was studied. Similar to PEO, FPEO is miscible with PVPh over the entire composition range. The hydrogen‐bonding interaction between FPEO and PVPh is as strong as that between PEO and PVPh as shown by Fourier‐transform infrared spectroscopy.     

Synthesis and Micellization Properties of Novel Symmetrical Poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) Triblock Copolymers

Summary: A four‐step strategy to synthesize well‐defined amphiphilic poly(ε‐caprolactone‐b‐[R,S] β‐malic acid‐b‐ε‐caprolactone) triblock copolymers [P(CL‐b‐MLA‐b‐CL)], which combines the anionic polymerization of [R,S] benzyl β‐malolactonate (MLABz), and the coordination‐insertion ring‐opening polymerization (ROP) of ε‐caprolactone (CL), followed by the selective removal of benzyloxy protective groups of the central poly(malolactonate) block is described. The first step involves MLABz initiated by potassium 11‐hydroxydodecanoate in the presence of 18‐crown‐6 ether. This step was carried out at 0 °C with an initial monomer concentration of 0.2 mol · L^?1 in order to limit the occurrence of undesirable transfer and termination reactions by proton abstraction. After selective reduction of the carboxylic acid end‐group of the resulting α‐hydroxy, ω‐carboxylic poly([R,S] benzyl β‐malolactonate) leading to an α,ω‐dihydroxy PMLABz, the polymerization of CL was initiated by each hydroxyl end‐groups previously activated by AlEt₃. Finally, after catalytic hydrogenation of the benzyl ester functions, the P(CL‐b‐MLA‐b‐CL) triblock copolymer was recovered and the amphiphilic character evidenced by UV spectroscopy. As demonstrated, the CMC of these new P(CL‐b‐MLA‐b‐CL) triblock copolymer is higher by one order of magnitude than that of a P(MLA‐b‐CL) diblock copolymer of similar composition.

Concentration dependence of pyrene I₃₃₈/I₃₃₅ intensitiy ratio for P(MLA‐b‐CL) diblock and P(CL‐b‐MLA‐b‐CL) triblock copolymers in water.